ac curent detector

alot of prints do not show the Rail supply lines to the IC's they assume you should know better.!

The first opamp in the circuit is the OTHER HALF of the LM1458 (which is a dual opamp). The power pins are shown on it, connecting to +12V and Gnd.

As mentioned in the other posts, the LM1458 is an 8-pin dual op amp. Even though the drawing shows two separate op amps, it's all one IC, and all eight pin connections are there.

As mentioned at the bottom of the circuit description

the circuit is set to have the second op amp (which is used as a comparator) turn on the transistor with a current of about 1/4 amp AC. Also, as he mentions in the writeup, you can increase the sensitivity by increasing the number of turns. You can also decrease the sensitivity by decreasing the number of turns. They're not directly proportional, though.

You should hook up a line cord to 4 ea. 100W bulbs, and reduce the number of turns until it just doesn't turn on. You will then have fairly reliable turn on at about 4 amps (or 480 watts at 120VAC). I would guess something around half the number of turns on the U-bolt would be a good start.

Magnet wire has a very thin enamel insulation, which is easily scratched. It isn't necessary to provide insulation between layers. However, it is very necessary to avoid winding over the threads of the U-bolt. The sharp edges of the threads will short out the insulation, and ruin your work. Make sure you use an iron U-bolt.

For a "real world" current detector, tape one end of a 6' zip cord to the U-bolt, then solder the ends of the wound magnet wire to the dressed leads of the zip cord. Also, be sure to at least tape the ends of the magnet wire down. Once you've got it working, a layer of tape all around might not be a bad idea. Copper wire of this diameter will break out of spite if you even look at it wrong. And for hobbyist stuff like this, electrical tape can be your friend.

Mr. Bowden's circuit is versatile, and can also be used to give a fairly accurate reading of peak AC current (by measuring the voltage across the second 10uF cap).

Good luck. Feel free to post again if you have any other questions or problems, or to let us know how it works.

Chris

We would be a lot more able to help you if you'd post a link to the circuit you're trying to build. The LM1458

What do you have on this thing so far?

Thanks, Rich